EXTENT OF PALEOZOIC CONTINENTAL SEAS 319 



statements are wholly untrue in theory and fact, but that, in the absence 

 of sufficient qualifications, they imply much greater diversity than ever 

 occurred in the interior continental areas. I object to them not only on 

 this account, but for the reason that such assertions logically suggest 

 difficulties in the way of determining the true chronological sequence, 

 hence in the way of practical correlation that either do not exist at all or 

 are much less formidable than they are made to appear. Even such broad 

 statements as "many a sandstone in New York and Pennsylvania is of 

 contemporaneous origin with a limestone in the Ohio and Mississippi 

 valleys" (Dana, page 398) are exaggerated if not actually untrue. Most 

 of the deposits thus referred to are either too thin or too obviously local 

 to be taken into account or they are not strictly synchronous, so that the 

 cases wherein such a statement is justifiable are really feiu, not "many." 



Of course, I have no wish to deny that "in all periods sand-beds, mud- 

 beds, clay-beds, pebble-beds, and limestone-beds have been simultaneously 

 in progress over different parts of the globe." I object only to the indis- 

 criminate application of this truth to all parts of the globe in all ages. 

 While admitting that similarly diverse sedimentation occurred at all 

 times on the globe, it yet seems clear that such diversity prevailed over 

 the whole globe, or some large part of it, only at times of great emer- 

 gence like the present. On the other hand, when and where the general 

 relief of the lands was low, diversity of conditions determining the local 

 character of deposits must have been correspondingly less, and in the 

 broad continental seas it seems never to have been very great, being in- 

 deed considerable in these only occasionally along the shores of newly 

 submerged land masses. Considering, finally, that the sedimentary 

 record accessible and known to the stratigrapher is almost confined to 

 these submergent phases, it will be clear that in the practical application 

 of the science the "difficulties" in correlation due to lateral variation of 

 deposits is much less than is commonly supposed. 



Reviewing the conditions that we may justly infer to have prevailed in 

 past geologic ages, the present differs sufficiently from the average to be 

 called abnormal. Depending on organic evidence, mild climates prevailed 

 throughout the northern hemisphere during a large majority of the dis- 

 tinguishable ages of which the marine record is preserved and accessible 

 in the continental basins. Regarding the intervening ages, some of which 

 must have been long and perhaps very different in climatic and other 

 features, too little is yet known of these to permit their adequate con- 

 sideration. Including, therefore, only the more or less well known as^es 

 in our comparison, the present seems abnormal (1) in the extreme differ- 

 entiation of climatic zones and (2) in the highly emergent attitude of 



